How Tongues Helped Vertebrates Conquer Land

[ intro ] Chances are you don’t give your tongue the
credit it deserves. That fleshy muscle in your mouth is so much
more than a food-tasting organ. Without tongues, we might still be swimming
around and staring longingly at the dry land we and
all other backboned animals never managed to conquer. So today, let’s take a trip through evolutionary
history to see how the humble tongue was key to world domination. The earliest vertebrates were fish, and fish
don’t have tongues. I know, you swear you’ve seen a fish with
a tongue. But I promise, you haven’t. Many fish have a structure called a basihyal: a raised lump of bone or cartilage sits at
the bottom of the mouth. It can look sort of like a tongue. But it doesn’t really move, and it has no
taste buds. So it’s not a true tongue— it’s just a tough shield to protect sensitive
nerves and blood vessels. And this all makes sense when you realize
that most animals with tongues use them for catching and swallowing food, and fish don’t need a mouth appendage for
that. Most have a neat trick called suction feeding. When a fish spots a tasty morsel, it swims up to it and explosively expands
its mouth. The top of the skull moves upward, the lower
jaw swings open, and a bony throat structure called the hyoid
moves down into the throat. All this causes a quick drop in water pressure
inside the fish’s mouth, and water rushes in, dragging the tasty morsel
into the mouth. Even fish that take bites of their prey often
employ a bit of suction to move things toward the throat. And those that don’t employ suction can
just open their mouths and swim to let water push things backwards. But, while all of this works great in water,
air is much less dense, so it doesn’t provide the force needed to
drag or shove prey down the throat. So fish were faced a problem as they expanded
their horizons. We know from the fossil record that one group
of bony fishes – the sarcopterygians – made the move to land between 400 and 350
million years ago, during the devonian period. Tetrapods—the legged animals that they became,
including all amphibians, reptiles, birds, and mammals— would go on to conquer the land, the sky,
and arguably, with us included, space. But first, they had to get out of the water. Fossils of early tetrapods like the famous
‘fishapod’ Tiktaalik reveal just how much needed to be tinkered with to make this transition, including changing up their limbs, backbones,
skulls, eyes, lungs and more. But they also had to change how they ate. Unfortunately, not a lot of fossil evidence
has been found for the early evolution of tongues, but by comparing fish to land-lubbers, we
can see where the change happened. It all has to do with that throat structure
I mentioned earlier: the hyoid. In fish, hyoid bones largely support muscles
of the gills. But tetrapods lack gills for the most part. So, the hyoid supports the muscles of the
tongue instead. We can even see this transition in action
in modern-day amphibians! Larval salamanders live in the water, and
their hyoid bones are part of their gill structure. When they metamorphose into adults, these
bones switch to supporting the tongue! As for how this shift from gill to tongue
happened… well, there are two main ideas. One hypothesis is that tongues first evolved
to help food move from the mouth into the throat. Picture an early tetrapod crawling along a
Devonian shoreline like a weird slimy crocodile. It snaps its jaws onto a small critter and
tilts its head back to drop the food into its mouth. A simple tongue would have been very helpful
just to move food to the right place. In salamanders that feed this way nowadays,
the hyoid drops down into the throat to move the tongue. Since this is the same motion the hyoid makes
during suction feeding in fish, this seems like a pretty straightforward evolutionary
step. But there’s another hypothesis that suggests
tongues first evolved to capture food instead. Lots of animals, such as salamanders and lizards,
poke out their sticky tongues to snatch up their food. A 2015 study found a similar strategy in an
unusual fish that uses a hydrodynamic tongue. That is, a tongue made of water! This study found that mudskippers carry along
a mouthful of water on their trips onto land. When they find food on the ground, they spit
the water all over it, then suck it all back up. It’s sort of a loophole that lets them suction-feed
on land. Kind of. And slow-motion X-ray video of the process
revealed that when the mudskippers spit the water out, their hyoid bone moved upward toward the mouth. That’s similar to the movement the hyoid
makes in salamanders that catch food by sticking out their tongues. So, perhaps early tetrapods developed a forward-moving
hyoid for water tongues, mudskipper style! Then, a soft, fleshy tongue eventually replaced
the fluid. As of now, we can’t say for sure if either
hypothesis is totally correct. It could even be that tongues as we know them
evolved multiple times! But we do know once our tetrapod ancestors
were armed with proper tongues, they were ready to feast all along ancient
shorelines. That still left whole continents to conquer! Like modern-day amphibians, early tetrapods
would have been restricted to environments with plenty of water available, partially because their eggs need to be laid
in water. But around 300 million years ago, one group
of tetrapods developed eggs with sturdy shells that could be laid in drier places. This group is known as the amniotes, and ultimately
gave rise to all reptiles and mammals. And as early amniotes moved into new environments,
they needed new tongues! Most amphibians have wet, squishy tongues. If they dry out, they can’t eat properly. Reptiles and mammals, on the other hand, tend
to have rough or scaly tongues covered in keratin, the same material that makes up your
hair and fingernails. This protects the tongue from losing moisture,
so these animals can feed in less humid places. So tongues allowed vertebrates to move onto
wet land, then wholly onto dry land, and thereby conquer every environment on Earth. So, be kind to your tongue. You owe it a lot. Thanks for watching this episode of SciShow! If you liked learning about tongues and how
weirdly important they are, you might like our episode looking at 7 of the weirdest ones
around today. And as always, don’t forget to subscribe! [ outro ]

These YouTube announcers need to standardize hand movements, like ASL does. A lot of announcers bounce open hands up & down and point occasionally – without any connection to the content except for providing visual rhythm. It looks stupid.

Great episode! Another Home Run! Michael is one of those few hosts that is able to really hold my attention, no matter the subject. I always enjoy reading the comments of fellow enthusiasts but I am afraid to on this scientific offering; I imagine a lot of immature remarks from those aspiring comedians will cloud the novel genuineness of this article.

.. wait, what? fish, the first animals to conquer land, were using tongues to eat… 'critters' on land? there's a logical gape hole there. tongue initially could only have been used to grab plant material on land.

Fish don't have tongues? Wait, what about Cymothoa Exigua? The tongue-eating louse? That horrific thing that crawls in through the fish's gills and lives in the fish's mouth after the tongue atrophies off from blood loss? Didn't you guys even do an episode about that?

So.. if the first land animals evolved tongues to catch critters.. where did the critters come from? I guess you specify vertebrates explicitly so some form of invertebrates were already crawling around the shore line by that point? Were we only one fish away from living in Nausicaa's forest?

So… here's an interesting question. Why do cetaceans still have tongues? Or is this just another one of those 'It doesn't get selected AGAINST so there's no reason to ditch it?' that is so common when it comes to vestigal traits?

he evolution of various body parts and essential systems that we rely on today are very good videos for younger kids. the simplified explanations you guys give are great and easy to understand for the younger kids as well, but leave just enough open ended information they can further research on their own. excellent job